Described below is a method for encoding data blocks for transmission in a radio communication system.
So-called “multicarrier” transmission methods, in which a plurality of carriers are simultaneously modulated, are becoming increasingly important in third-generation and fourth-generation mobile radio networks. One typical multicarrier transmission method is the so-called “Orthogonal Frequency Division Multiplexing (OFDM)” radio transmission method in which carriers which are referred to as “subcarriers” are used to transmit symbols. A multicarrier transmission method affords the advantage of high-data-rate transmission with little receiver complexity. In addition, it is very robust to temporal fluctuations in properties of the radio transmission channel.
Radio transmission resources, which are referred to as so-called “chunks”, are used in a multiplicity of radio transmission methods—thus during OFDM radio transmission as well. A “chunk” is dimensioned, on the one hand, by a number of multicarriers or subcarriers and, on the other hand, by a defined time slot which can be assigned to the multicarriers or subcarriers. For example, a plurality of adjacent subcarriers are used to dimension a “chunk”.
In these methods, a limited number of bits is assigned to each radio transmission resource for the purpose of transmission. Additional control information which is concomitantly transmitted as a so-called “signaling overhead” is in turn assigned to the bits of a radio transmission resource. Such control information disadvantageously reduces a throughput of useful data which is referred to as the “payload”.
The dimensions of a “chunk” are determined on the basis of properties of the radio transmission channel. The properties of the radio transmission channel are determined using channel estimation methods, for example. Depending on the properties of the radio transmission channel, a transmission power and/or selected modulation of the transmission signal is/are adapted at the transmitter end and suitable subcarriers or multicarriers are selected.
A “chunk” under consideration is advantageously dimensioned with regard to so-called “flat fading” in the frequency domain and a constant temporal behavior in the time domain. The dimensioning makes it possible to adapt the radio transmission to be carried out to the properties of the radio transmission channel in an adaptive manner.
So-called “quality of service (QoS)” requirements which depend on wishes and selected services of a subscriber must also be complied with during radio transmission.
Encoding methods or error correction codes are used to adapt the radio transmission to the properties of the radio transmission channel in an adaptive manner and to meet the QoS requirements. In this case, a throughput of useful data which can be achieved depends on the encoding method used since a large number of redundancy bits must be transmitted, for example, in the case of very secure data transmission with a complex error correction code.
If a so-called “turbocode (TC)” or a so-called “Low Density Parity Check Code (LDPC)” is used, for example, for encoding, a relatively long code sequence is required for good-quality transmission.
If low-level modulation, for example BSPSK modulation, is used during OFDM radio transmission, only a maximum number of 64 bits per “chunk” can thus be transmitted.
As regards this maximum number of bits, a short code sequence could be used to encode the bits but this could result in a loss of data during transmission.
If, in contrast, a long code sequence is intended to be used and the encoded bits are then divided among the “chunks”, a suitable code length for respective modulation operations could be found only with difficulty. Independent adaptation of encoding, on the one hand, and modulation which can be set in an adaptive manner, on the other hand, are possible only with difficulty for desired optimum transmission of useful data.
For the purpose of encoding, a number of error correction codes with different code lengths are typically provided and a compromise is made between the possibility of correcting errors, on the one hand, and delays when transmitting the useful data as part of the QoS requirements, on the other hand. Data blocks are then encoded and are mapped to, or divided among, available “chunks”.